1. Field of the Invention
This invention relates to apparatus for sensing infrared or other electromagnetic radiation, and in particular, to a Schottky barrier photodiode having a grooved upper surface to increase detection efficiency.
2. Description of the Prior Art
Applications for remote sensing have expanded enormously over the past 20 years. Such technology has wide application for the detection, measurement, and analysis of natural and man-made objects remotely situated from the observer. The detection of infrared radiation is one aspect of remote sensing particularly useful for night vision and satellite imaging.
To detect infrared radiation, several types of devices have been developed. These include intrinsic semiconductors such as mercury-cadmium-tellurium, extrinsic semiconductors such as gallium- or indium-doped silicon, and Schottky barrier photodiodes such as palladium silicide on silicon. While each of these devices finds particular application, the use of Schottky barrier photodiodes has been limited because of their low quantum efficiency.
A typical prior art Schottky barrier photodiode infrared detector is a planar device. Usually, the device includes a layer of metal silicide on the upper surface of a silicon body. The silicide is overlaid by insulating material and a mirror. Infrared radiation directed onto the lower surface of the silicon body passes through the silicon, through the metal silicide, reflects off the mirror, and returns through the metal silicide. As the light passes through the silicide, it causes holes or electrons (depending upon the conductivity type of the substrate) to be injected into the substrate for collection and detection using conventional charge-coupled device technology or MOS readout technology. One such Schottky barrier photodiode is shown in the article by R. C. McKee, "Enhanced Quantum Efficiency of Pd.sub.2 Si Schottky Infrared Diodes on &lt;111&gt; Si," IEEE Transactions on Electron Devices (July 1984) ED-31(7), p. 968. Unfortunately, such prior art devices have very low quantum efficiencies; for example, the quantum efficiency of platinum silicide is usually under 2% in the desired 3 to 5 micron wavelength range, and under 1% at 4 microns.